Agnosia A - ACNR

1 18 IACNR VOLUME 4 NUMBER 5 NOVEMBER/DECEMBER 2004 AgnosiaAgnosia is a perceptual disorder in which sensationis preserved but the ability to recognise a stimulusor know its meaning is lost. Agnosia means with-out knowledge . Patients with Agnosia cannot under-stand or recognise what they see, hear or feel. Agnosiaresults from lesions that disconnect and isolate visual,auditory and somatosensory input from higher level pro-cessing. Perceptual skills have a hierarchical and nature and severity of perceptualimpairment depends upon modality affected and thelevel at which sensory processing has been is rare in its pure form.

2 Less than one percent of allneurological patients have assessingagnosia, it is important to establish that sensation is pre-served; the patient is alert, intelligence is intact (or nearintact) with no language or memory involves assessing what the patient sees,hears or feels when presented with objects, pictures orsounds using a combination of clinical procedures andneuropsychological (1890) made a distinction between a deficit inthe ability to perceive stimuli consciously and a deficitreflecting an inability to ascribe meaning to what is per-ceived, a disorder he referred to as Seelenblindheit, or soulblindness.

3 2In current literature, a distinction is madebetween apperceptive Agnosia and associative Agnosia describes a failure in object recog-nition primarily due to problems in early stage perceptu-al processing. Associative Agnosia refers to a disorderwhen early stage perceptual processing is intact; thepatient can develop a percept of an object but is unable toaccess memory or knowledge of the object. The object isperceived as an object but it has no meaning. Research hasled to more refined taxonomies. Most cases of associativeagnosia probably have deficits in early stage processingand perceptual and memory representations in objectrecognition are not clearly ,4 Boundaries ofapperceptive Agnosia and associative Agnosia are not asclear as once thought, although the classification remainsuseful.

4 Agnosia is classified according to modality:- Visual Auditory TactileVisual AgnosiaVisual Agnosia is a deficit in object recognition confinedto the visual modality, despite intact elementary visualprocesses and which is not due to problems in language,memory or intellectual decline. It is the most commonand best understood form of Agnosia . There are twobroad categories; apperceptive visual Agnosia and associa-tive visual Visual AgnosiaApperceptive visual Agnosia is characterised by an intactvisual ability on a basic sensory level, but a defect in earlystage visual processing prevents a correct percept of thestimulus being formed.

5 The patient is unable to access thestructure or spatial properties of a visual stimuli and theobject is not seen as a whole or in a meaningful , anoxia and carbon monoxide poisoning are com-mon causes and it is often associated with diffuse, poste-rior lesions. Patients fail tests such as visual matching, dis-criminating shapes, comparing similar figures and copy-ing drawings. Useful tests are incomplete letters, objectdecision and silhouettes sub-tests from the VisualOrientation and Space Perception Battery (VOSP), theGollin Figures and usual/unusual views test fromBirmingham Object Recognition Battery (BORB).

6 5,6Dr Eric Ghadiali is ConsultantClinical Neuropsychologist at TheWalton Centre for Neurology founded theDepartment ofClinicalNeuropsychology in 1979 anduntil 2004 was Head ofDepartment. He divides his timebetween clinical practice andmedico-legal and forensic neu-ropsychology. His current inter-ests are head injury, dementia,Parkinson s disease, chronic painand medical to:Dr E J Ghadiali,Consultant ClinicalNeuropsychologist,Department of ClinicalNeuropsychology,The Walton Centre for Neurologyand Neurosurgery,Lower Lane,Fazakerley,Liverpool,L9 : PrimerFigure 1: It is essential to rule out memory problems when 2:Tests for apperceptive visual Agnosia (from VOSP);(a) incomplete letters (b) object decision.

7 Patient is shown four silhouettedrawings and has to identify which one of the four is a real 3:Tests for associative visualagnosia (from BORB).Patient is required to identify real andunreal VOLUME 4 NUMBER 5 NOVEMBER/DECEMBER 2004I19 Associative Visual AgnosiaIn associative visual Agnosia , primary sensory and earlyvisual processing systems are preserved. The patient canperceive objects presented visually but cannot interpret,understand or assign meaning to the object, face or visual Agnosia is usually the result of bilateraldamage to the inferior temporo-occipital junction andsubjacent white matter.

8 The cause is most often infarctionof the posterior cerebral artery bilaterally. Other causesinclude tumour, haemorrhage and demyelination. It ismore common than apperceptive visual sub-types are:- Visual object Agnosia Patients are able to copy objects and pictures, often withgreat accuracy, but do not recognise the objects or under-stand what they have drawn. This can be assessed by pre-senting the patient with pictures of objects and askingthem to name, describe functions and sort according touse or category to which they belong.

9 Analysis of errorswill enable the examiner to exclude anomia and semanticmemory problems, both of which can cause naming andrecognition problems. For example, a patient with visualobject Agnosia will be unable to name or recognise a pic-ture of a kangaroo. The same patient will have no difficul-ty naming and describing the characteristics of a kangarooif requested via the auditory modality. Patients withanomia will be unable to name the picture and mayrespond, it s found in Australia, it t think ofits name, demonstrating intact recognition.

10 Patients withsemantic dementia have central loss of knowledge and willbe unable to name the picture or demonstrate any knowl-edge of the object regardless of modality. The GradedNaming Test provides a source of pictures of objects fromdifferent tests are the real/unreal objecttest from the Birmingham Object Recognition Battery andThe Pyramid and Palm Trees test, a matching test thatrequires the patient to select one of two pictures connect-ed with the target content is minimal mak-ing it suitable for patients with aphasia. SimultanagnosiaSimultanagnosia is characterised by an inability to per-ceive more than one aspect of a visual stimulus and tointegrate visual detail into a coherent whole.